Satellite communications systems and methods are widely used for radiotelephone communications. Satellite communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is/are configured to wirelessly communicate with a plurality of wireless terminals.
A satellite communications system or method may utilize a single antenna beam or antenna pattern covering an entire area served by the system. Alternatively, or in combination with the above, in cellular satellite communications systems and methods, multiple beams (cells or antenna patterns) are provided, each of which can serve a substantially distinct geographic area in an overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular radiotelephone systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with wireless terminals over a bidirectional communications pathway, with wireless terminal communications signals being communicated from the satellite to a wireless terminal over a downlink or forward link (also referred to as a forward service link), and from the wireless terminal to the satellite over an uplink or return link (also referred to as a return service link).
The overall design and operation of cellular satellite communications systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “wireless terminal” includes devices which include a radio frequency transceiver, such as cellular and/or satellite radiotelephones; Personal Communications System (PCS) terminals that may combine a radiotelephone with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “wireless terminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion over one or more terrestrial and/or extraterrestrial locations. A wireless terminal also may be referred to herein as a “radiotelephone,” “radioterminal,” “mobile terminal,” “mobile user terminal,” “user device” or simply as a “terminal”. Furthermore, as used herein, the term “space-based” component includes one or more satellites and/or one or more other objects/platforms (e.g., airplanes, balloons, unmanned vehicles, space crafts, missiles, etc.) that have a trajectory above the earth at any altitude. In addition, as used herein the term “canceling” or “cancellation” as relating to interference canceling or cancellation means complete elimination of at least one component/element of the interference and/or at least a reduction of at least one component/element of the interference.
A terrestrial network that is configured to provide wireless communications by using and/or reusing at least some of the frequencies authorized for use by a satellite system can enhance the availability, efficiency and/or economic viability of the satellite system. Specifically, it is known that it may be difficult for satellite communications systems to reliably serve densely populated areas, because satellite signals may be blocked by high-rise structures and/or may not effectively penetrate into buildings. As a result, the satellite spectrum may be underutilized or unutilized in such areas. The terrestrial use and/or reuse of at least some of the satellite system frequencies can reduce or eliminate this potential problem.
Moreover, a capacity measure of an overall system, including a terrestrially-based and a space-based network, may be increased by the introduction of terrestrial frequency use/reuse of at least some of the frequencies authorized for use by the space-based network, since terrestrial frequency use/reuse may be much denser than that of a satellite-only (space-based network only) system. In fact, capacity may be enhanced where it may be most needed, i.e., in densely populated urban/industrial/commercial areas. As a result, the overall system may become more economically viable, as it may be able to serve a larger subscriber base more effectively and reliably.
One example of terrestrial reuse of satellite frequencies is described in U.S. Pat. No. 5,937,332 to Karabinis entitled Satellite Telecommunications Repeaters and Retransmission Methods, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described therein, satellite telecommunications repeaters are provided which receive, amplify, and locally retransmit the downlink/uplink signal received from a satellite/radioterminal thereby increasing the effective downlink/uplink margin in the vicinity of the satellite telecommunications repeaters and allowing an increase in the penetration of uplink and downlink signals into buildings, foliage, transportation vehicles, and other objects which can reduce link margin. Both portable and non-portable repeaters are provided. See the abstract of U.S. Pat. No. 5,937,332.
Radioterminals for a satellite communications system or method having a terrestrial communications capability by terrestrially using and/or reusing at least some of the frequencies of a satellite frequency band that is also used, at least in part, by the radioterminals for space-based communications, wherein the radioterminals are configured to communicate terrestrially and via a space-based component by using substantially the same air interface for both terrestrial and space-based communications, may be more cost effective and/or aesthetically appealing than other alternatives. Conventional dual band/dual mode wireless terminal alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite/terrestrial wireless terminals, duplicate some components (as a result of the different frequency bands and/or air interface protocols between satellite and terrestrial communications), which may lead to increased cost, size and/or weight of the wireless terminal. See U.S. Pat. No. 6,052,560 to Karabinis, entitled Satellite System Utilizing a Plurality of Air Interface Standards and Method Employing Same.
Satellite communications systems and methods that may employ terrestrial reuse of satellite frequencies are described in U.S. Pat. No. 6,684,057 to Karabinis, entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum; and Published U.S. Patent Application Nos. US 2003/0054760 to Karabinis, entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum; US 2003/0054761 to Karabinis, entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies; US 2003/0054814 to Karabinis et al., entitled Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0073436 to Karabinis et al., entitled Additional Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0054762 to Karabinis, entitled Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems and Methods; US 2003/0153267 to Karabinis, entitled Wireless Communications Systems and Methods Using Satellite-Linked Remote Terminal Interface Subsystems; US 2003/0224785 to Karabinis, entitled Systems and Methods for Reducing Satellite Feeder Link Bandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 to Karabinis et al., entitled Coordinated Satellite-Terrestrial Frequency Reuse; US 2002/0090942 to Karabinis et al., entitled Integrated or Autonomous System and Method of Satellite-Terrestrial Frequency Reuse Using Signal Attenuation and/or Blockage, Dynamic Assignment of Frequencies and/or Hysteresis; US 2003/0068978 to Karabinis et al., entitled Space-Based Network Architectures for Satellite Radiotelephone Systems; US 2003/0143949 to Karabinis, entitled Filters for Combined Radiotelephone/GPS Terminals; US 2003/0153308 to Karabinis, entitled Staggered Sectorization for Terrestrial Reuse of Satellite Frequencies; and US 2003/0054815 to Karabinis, entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns In Response to Terrestrial Reuse of Satellite Frequencies, all of which are assigned to the assignee of the present invention, the disclosures of all of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Some satellite communications systems and methods may employ interference cancellation techniques to allow increased terrestrial use/reuse of satellite frequencies. For example, as described in U.S. Pat. No. 6,684,057 to Karabinis, cited above, a satellite communications frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell that is using the satellite communications frequency for space-based communications, using interference cancellation techniques. Moreover, the ancillary terrestrial network can use a modified range of satellite band forward link frequencies for transmission, to reduce interference with at least some out-of-band receivers. A modified range of satellite band forward link frequencies that is used by the ancillary terrestrial network can include only a subset of the satellite band forward link frequencies to provide a guard band between frequencies used by the ancillary terrestrial network and frequencies used by out-of-band receivers, can include power levels that monotonically decrease as a function of increasing/decreasing frequency and/or can include two or more contiguous slots per frame that are left unoccupied and/or are transmitted at reduced maximum power. Time division duplex operation of the ancillary terrestrial network may also be provided over at least a portion of the satellite band return link frequencies. Full or partial reverse mode operation of the ancillary terrestrial network also may be provided, where at least some of the forward link and return link frequencies are interchanged with the conventional satellite forward link and return link frequencies. See the Abstract of U.S. Pat. No. 6,684,057.